Neuropeptide Y (NPY) is a 36-amino acid-containing peptide that is contained within synpathetic nerve terminals and co-released with norepinephrine to produce vasoconstriction. NPY18-36 is a fragment of NPY that, in contrast to NPY, produces a decrease of blood pressure and cardiac output. The purpose of this grant is threefold: (1) to characterize an NPY antagonist to study the physiology of endogenous NPY; (2) to study the actions of NPY on endothelial cell release of endothelin and to determine the role of endothelin in mediating the cardiovascular actions of NPY; and (3) to determine if NPY18-36 is present in animals. NPY analogs wi)) be evaluated in one or more of three systems: (1) binding to bovine aorta endothelial cells (BAEC) to assess structural requirements for receptor binding; (2) stimulation of endothelin release from BAEC to assess intrinsic activity in vitro; and (3) effects on blood pressure and heart rate in awake rats as an index of vasoconstrictive activity. Passive immunization and/or an NPY receptor antagonist will be used to determine the role of endogenous NPY in three systems: (1) changes in pancreatic blood flow following electrical stimulation of the pancreatic nerve; (2) regulation of blood pressure following alpha-adrenergic blockade; and (3) regulation of blood pressure following 30% hemorrhage. An endothelin radioimmunoassay (RIA) will be used to measure the release of endothelin from BAEC's following NPY treatment. The role of NPY-induced endothelin release in mediating NPY's effects on blood pressure will be assessed using passive immunization. The presence of the NPY fragment, NPY18-36, in animals will be evaluated by extraction of peptides from blood, brain, heart and spleen and measurement of NPY18-36 by RIA. Authenticity of endogenous NPY18-36 will be assessed by using high pressure liquid and gel filtration chromatography. This grant will define antagonists and cellular actions, i.e., role of endothelin, of NPY. In addition, the presence of an NPY fragment with unique biological actions, NPY18-36, will be determined. Each of these goals provides new and important infor- mation on the biochemistry of cardiovascular regulation. Antagonists of NPY will provide new ways to study and perhaps treat cardiovascular dysfunction in man.